KR20200134258A - Copper-ceramic substrate - Google Patents

Abstract

The present invention relates to a copper-ceramic substrate 1, wherein the copper-ceramic substrate 1 has-a ceramic carrier 2, and-a free surface for forming a conductor structure and/or for fixing the bonding wires. , At least one copper layer (3, 4) bonded to the surface of the ceramic carrier (2), the copper layer (3, 4) has an average particle size diameter of 200 to 500 ㎛, preferably 300 to 400 ㎛ Branches have a microstructure.

Description

Copper-ceramic substrate

The present invention relates to a copper-ceramic substrate having the features of the preamble according to claim 1.

Copper-ceramic substrates (eg, DCB, AMB) are used to manufacture electronic power modules, for example, and are composites of ceramic carriers with copper layers on one or both sides. The copper layer is pre-made from a semi-finished copper product in the form of a copper foil, usually 0.1 to 1.0 mm, and is connected to the ceramic carrier using a connection method. This connection method is also known as DCB (direct copper bonding) or AMB (active metal brazing). However, in the case of a high strength ceramic carrier, a copper ply or a layer of copper having a thicker thickness can also be applied, which is basically advantageous in terms of electrical and thermal properties.

For example, a ceramic plate made of mullite, Al ₂ O ₃ , Si ₃ N ₄ , AlN, ZTA, ATZ, TiO ₂ , ZrO ₂ , MgO, CaO, CaCO ₃ , or a mixture of at least two of these materials is ceramic. It is used as a carrier.

In the DCB method, a copper ply is connected to the ceramic base using the following method steps:

-Oxidizing the copper ply in a way that results in a uniform copper oxide layer;

-Placing the copper ply on the ceramic carrier;

-Heating the composite to a process temperature of 1060 °C to 1085 °C.

This creates a eutectic melt in the copper ply, which forms a material-to-material bond with the ceramic carrier. This process is known as bonding. When Al ₂ O ₃ is used as the ceramic carrier, a thin Cu-Al spinel layer is produced by bonding.

After the bonding process, the required conductor tracks are structured by etching the outer facing surface of the copper ply, ie the free surface of the copper ply. Subsequently, the chip is soldered and a connection to the contact on each upper side of the chip is made by applying a bonding wire, and for this purpose the microstructure of the free surface of the copper layer should be homogeneous and structured as precisely as possible. Should be. Then, in order to produce the power module, a copper-ceramic substrate may be additionally connected to the base plate.

The advantages of the described copper-ceramic substrate are, among other things, the large current-carrying ability of copper, and good electrical insulation and mechanical support from the ceramic carrier. In addition, the DCB technology allows the copper ply to adhere well to the ceramic carrier. In addition, the copper-ceramic substrates used are stable at the high ambient temperatures often present in applications.

The weakness of copper-ceramic substrates is the so-called thermal shock resistance, a material parameter that accounts for the failure of a component after a certain number of transient thermal induced stresses. These parameters are important to the useful life of the power module, as extreme temperature gradients result during module operation. Due to the different coefficients of thermal expansion of the ceramic material and copper material used, mechanical stress is thermally induced during use in a copper-ceramic substrate, which, after a certain number of cycles, causes the layer separation of the copper layer from the ceramic layer ( delamination) and/or cracking in the ceramic layer and/or the copper layer, resulting in component failure.

In general, copper-ceramic substrates having a copper layer with a fine microstructure generally have advantages with respect to optical inspection, bonding ability, etching behavior, grain boundary formation, galvanisability, and further processing. Is advantageous in However, in the case of temperature fluctuations, due to the large thermal induced stress, the useful life is shortened and has a disadvantage of having poor resistance to temperature changes.

Conversely, a copper-ceramic substrate having a copper layer with a coarser microstructure has the advantage of a long useful life, but has the disadvantages associated with the additional requirements described above.

DE 10 2015 224 464 A1 discloses a copper-ceramic substrate in which the microstructure of the copper layer on the side facing the ceramic carrier intentionally has a larger particle size than at the free surface.

The advantage of this solution is that due to the small particle size of the microstructure, the copper layer on the free surface can be structured lightly and very finely, while the copper layer on the side facing the ceramic carrier, the larger particle size. Due to this, it can be confirmed from the fact that it has better thermal shock resistance according to the Hall-Petch relationship. Accordingly, the copper-ceramic substrate can be improved in a way that has better properties with respect to the different requirements described above. The selection of the target particle size on both sides of the copper layer creates a new design parameter that allows the copper-ceramic substrate to be designed in an improved manner with respect to both requirements.

A disadvantage of this solution can be seen in the fact that the implementation of different particle sizes requires additional effort. For example, in order to realize different particle sizes, it is conceivable to produce a copper layer by plating two different copper layers with different particle sizes, which represents an additional workload associated with cost. As a result, the copper-ceramic substrate of DE 10 2015 224 464 A1 becomes more expensive and is therefore suitable only for special applications that can afford a higher price.

In connection with this background, it is an object of the present invention to provide a copper-ceramic substrate that can be produced more cost-effectively than the copper-ceramic substrate from publication DE 10 2015 224 464 A1 and can nevertheless satisfy various requirements. Is to do.

According to the present invention, in order to achieve the above object, a copper-ceramic substrate having the features of the preamble according to claim 1 is proposed. Further desirable improvements will be found in the dependent claims.

According to the basic idea of the invention, it is proposed that the copper layer has a microstructure with an average particle size diameter of 200 to 500 μm, preferably 300 to 400 μm.

The microstructured particles not only need to have a particle size within the suggested range in this case; The distribution of particle size corresponds to a monomodal Gaussian distribution, and a small proportion of the particles may also have a particle size of less than or greater than 200 or 500 μm or less than or greater than 300 μm or 400 μm. It is only important that the average particle size is within the suggested range. The particle size diameter can be determined, for example, using the linear intercept method described in ASTM 112-13. However, particles with a particle size larger than 1000 μm should be avoided in any case.

The proposed microstructure of the copper layer is, for example, by complying with a predetermined throughput or dwell time and by the choice of temperature at the lead and lag of the bonding process. , Or can also be realized directly during bonding on the ceramic carrier by means of a separate temperature post-treatment.

The advantage of the proposed copper-ceramic substrate can be confirmed in the fact that the substrate has a sufficiently long useful life, which by choosing the average particle size diameter, the particles have an average size, and by the above, the hole- This is because, according to the fetch relation, a sufficiently low stress level is realized in the substrate during temperature-induced alternating bending loads occurring under normal use to achieve the desired long useful life. In addition, requirements for bonding properties, requirements for optical inspection, requirements for etching or cutting processes necessary to introduce conductor structures, and additional specific requirements may be met, for this purpose less than 500 μm or particularly preferably 400 An average particle size of less than μm is advantageous.

In order to achieve these advantageous properties of the microstructure of the copper layer after the temperature treatment process,

-Copper layer

It is additionally proposed to have a proportion of at least 99.95% Cu, preferably at least 99.99% Cu.

In addition, the copper layer is preferably

-It can have a ratio of Ag less than 25 ppm.

According to a further preferred embodiment, the copper layer is

-It may have a ratio of O of 10 ppm or less, preferably 5 ppm or less.

It is additionally proposed that the copper layer, in each case, has a proportion of Cd, Ce, Ge, V, Zn elements of 0 to 1 ppm or less,

-According to a further preferred embodiment, the copper layer as a whole has a proportion of elements Cd, Ce, Ge, V, Zn of at least 0.5 ppm and not more than 5 ppm.

It is additionally proposed that the copper layer, in each case, has a ratio of Bi, Se, Sn, Te elements of 0 to 2 ppm or less,

-According to a further preferred embodiment, the copper layer as a whole has a ratio of Bi, Se, Sn, Te elements of at least 1.0 ppm and not more than 8 ppm.

It is additionally proposed that the copper layer, in each case, has a proportion of Al, Sb, Ti, Zr elements of 0 to 3 ppm or less,

-According to a further preferred embodiment, the copper layer as a whole has a proportion of elements Al, Sb, Ti, Zr of at least 1.0 ppm and not more than 10 ppm.

It is additionally proposed that the copper layer, in each case, has a ratio of elements As, Co, In, Mn, Pb, Si of 0 to 5 ppm or less,

-According to a further preferred embodiment, the copper layer as a whole has a ratio of elements As, Co, In, Mn, Pb, Si of at least 1.0 ppm and not more than 20 ppm.

It is additionally proposed that the copper layer, in each case, has a proportion of B, Be, Cr, Fe, Mn, Ni, P, S elements of 0 to 10 ppm or less,

-According to a further preferred embodiment, the copper layer has a proportion of elements B, Be, Cr, Fe, Mn, Ni, P, S as a whole of at least 1.0 ppm and not more than 50 ppm.

It is further proposed that the copper layer has a proportion of the elements referred to in claims 4 to 16, which additionally contains impurities of preferably 50 ppm or less.

Hereinafter, the present invention will be described based on preferred embodiments with reference to the accompanying drawings.

1 is a copper-ceramic substrate according to the present invention with two copper layers.

The power module is a semiconductor component of a power electronic device and is used as a semiconductor switch. The power module includes a plurality of power semiconductors (chips) that are electrically insulated from a heat sink in one housing. The power module is applied to the metallized surface of the electrically insulating plate (e.g. made of ceramic) by soldering or bonding to ensure heat conduction to the base plate on the one hand and electrical insulation on the other. do. The composite of the metallized layer and the insulating plate is referred to as a copper-ceramic substrate, and is realized on an industrial scale using the so-called DCB technology (direct copper bonding technology).

The chips are contacted by bonding using thin bonding wires. In addition, additional modules (eg, sensors, resistors) with different functions may exist and may be integrated.

To produce a DCB substrate, ceramic carriers (eg, Al ₂ O ₃ , Si ₃ N ₄ , AIN, ZTA, ATZ) are bonded up and down to each other using a copper ply in a bonding process. In preparation for this process, the copper plies can be surface-oxidized (eg, chemically or thermally) before being placed on the ceramic carrier, and then placed on the ceramic carrier. In a high temperature process between 1060° C. and 1085° C. a connection is created, and a process melting is created on the surface of the copper ply, which forms a connection with the ceramic carrier. For example, in the case of copper (Cu) on aluminum oxide (Al ₂ O ₃ ), this connection consists of a thin layer of Cu-Al spinel.

1 shows a copper-ceramic substrate 1 further developed according to the invention with a ceramic carrier 2 and two copper layers 3 and 4. The two copper layers 3 and 4 further developed according to the invention have a microstructure having an average particle size diameter of 200 to 500 μm, preferably 300 to 400 μm.

The copper layers 3 and 4 are, for example, in the introduction, so that the copper layers 3 and 4 are connected to the ceramic carrier 2 by a material-to-material bond in the respective surface edge regions 5 and 6 By means of the described DCB method, it can be connected to the ceramic carrier 2.

During the DCB method, the copper layers 3 and 4 are placed on a ceramic carrier 2 in the form of a pre-oxidized semi-finished copper product and then heated to a process temperature of 1060°C to 1085°C. The Cu-oxydul in the copper layers 3 and 4 melts and forms a connection with the ceramic carrier 2 in the surface edge regions. Due to the influence of temperature and recrystallization of the two copper materials, the microstructure can be set by selecting an appropriate residence time and cooling time so that the desired average grain size diameter is automatically set. Since the effects of temperature treatment including cooling processes are well known to those skilled in the art, one of ordinary skill in the art can specifically select parameters such that a microstructure is formed in accordance with the present invention without the need for additional temperature treatment. In case the bonding process does not allow the above setting, or if this is not desirable for economic reasons, the microstructure can also be achieved by means of a temperature treatment carried out subsequently or carried out in advance. Further, the copper layers 3 and 4 preferably have a Vickers hardness of 40 to 100 after bonding.

The copper layers 3 and 4 having the microstructure according to the invention or having the ratio proposed according to the invention and in particular the proposed ratio of O are very conductive Cu materials, 50 MS/m, preferably at least 57 MS/m and particularly preferably at least 58 MS/m. However, materials of lower conductivity may also be considered. In addition, if the material properties of the copper layers 3 and 4 are further improved and thereby the microstructure according to the invention is not negatively affected, the copper layers 3 and 4 are also, if necessary, additional Cu materials or layers. Can be supplemented by

The semi-finished copper products of the copper layers 3 and 4 can have a thickness of 0.1 to 1.0 mm, are placed on the ceramic carrier 2 in large dimensions and connected to the ceramic carrier 2 by the DCB method. . Subsequently, a large area copper-ceramic substrate 1 is cut into smaller units and further processed.

The copper layers 3 and 4 may additionally have at least 99.95% Cu, preferably at least 99.99% Cu, 25 ppm or less Ag, 10 ppm or less or preferably 5 ppm or less O.

Further, the copper layers 3 and 4 are in each case 0 to 1 ppm or less of the ratio of Cd, Ce, Ge, V, Zn elements, and/or in each case, 0 to 2 ppm Bi, The proportion of elements Se, Sn, Te, and/or in each case, 0 to 3 ppm or less of the Al, Sb, Ti, Zr elements, and/or in each case 0 to 5 ppm or less As, Co , In, Mn, Pb, Si elements, and/or in each case 0 to 10 ppm or less of B, Be, Cr, Fe, Mn, Ni, P, S elements. The additional elements listed may be intentionally introduced into the microstructure by doping during the melting process immediately after casting, or the elements may already be present in the copper layers 3 and 4 during the production of semi-finished copper products. In any case, the proportion of the element, including additional impurities, should preferably be 50 ppm or less.

In addition, the copper layer according to a further preferred embodiment has a ratio of Cd, Ce, Ge, V, Zn elements of at least 0.5 ppm and 5 ppm or less, and a ratio of Bi, Se, Sn, Te elements of at least 1.0 ppm and 8 ppm or less. , At least 1.0 ppm and 10 ppm or less of Al, Sb, Ti, Zr elements, at least 1.0 ppm and 20 ppm or less of As, Co, In, Mn, Pb, Si elements, at least 1.0 ppm and 50 ppm in total It has the following ratio of B, Be, Cr, Fe, Mn, Ni, P, and S elements.

Quantitative proportions of the elements described herein are essential in achieving the average particle size of the microstructure proposed according to the invention. Microstructure formation is caused, in particular, due to the reduction of secondary recrystallization in the microstructure during the bonding process and grain improvement of the microstructure caused by the element. For example, the element As can change the recrystallization temperature and, in particular, increase the recrystallization temperature, so that the microstructure is no longer in the bonding process, to the extent that the average grain size increases and therefore falls outside the proposed range. Does not change during In addition, the Zr element can be used to preserve the microstructure while maintaining the average particle size when exposed to temperature, because Zr acts as an external seed.

Claims (17)

-Ceramic carrier 2, and
-A copper-ceramic substrate comprising at least one copper layer (3, 4) bonded to the surface of the ceramic carrier (2), having a free surface for forming a conductor structure and/or for fixing the bonding wires In (1),
-A copper-ceramic substrate (1), characterized in that the copper layers (3, 4) have a microstructure having an average particle size diameter of 200 to 500 µm, preferably 300 to 400 µm. The method of claim 1,
-A copper-ceramic substrate (1), characterized in that the copper layer (3, 4) has an electrical conductivity of at least 50 MS/m, preferably at least 57 MS/m and particularly preferably at least 58 MS/m. The method according to claim 1 or 2,
-A copper-ceramic substrate (1), characterized in that the copper layers (3, 4) have a Vickers hardness of 40 to 100. The method according to any one of claims 1 to 3,
Copper-ceramic substrate (1), characterized in that the copper layers (3, 4) have a proportion of at least 99.95% Cu, preferably at least 99.99% Cu. The method of claim 4,
-A copper-ceramic substrate (1), characterized in that the copper layers (3, 4) have a ratio of Ag of 25 ppm or less. The method according to claim 4 or 5,
-A copper-ceramic substrate (1), characterized in that the copper layers (3, 4) have a ratio of O of 10 ppm or less, preferably 5 ppm or less. The method according to any one of claims 4 to 6,
A copper-ceramic substrate (1), characterized in that the copper layers (3, 4) have, in each case, a ratio of Cd, Ce, Ge, V, Zn elements of 0 to 1 ppm or less. The method of claim 7,
-The copper-ceramic substrate (1), characterized in that the copper layers (3, 4) have a total ratio of Cd, Ce, Ge, V, Zn elements of at least 0.5 ppm and 5 ppm or less. The method according to any one of claims 4 to 8,
The copper-ceramic substrate (1), characterized in that the copper layers (3, 4), in each case, have a ratio of Bi, Se, Sn and Te elements of 0 to 2 ppm or less. The method of claim 9,
-The copper-ceramic substrate (1), characterized in that the copper layers (3, 4) have a ratio of Bi, Se, Sn and Te elements of at least 1.0 ppm and 8 ppm as a whole. The method according to any one of claims 4 to 10,
-A copper-ceramic substrate (1), characterized in that the copper layers (3, 4) have, in each case, a ratio of Al, Sb, Ti and Zr elements of 0 to 3 ppm or less. The method of claim 11,
-The copper-ceramic substrate (1), characterized in that the copper layers (3, 4) have a ratio of Al, Sb, Ti and Zr elements of at least 1.0 ppm and 10 ppm or less as a whole. The method according to any one of claims 4 to 12,
-A copper-ceramic substrate (1), characterized in that the copper layers (3, 4) have, in each case, a ratio of elements As, Co, In, Mn, Pb, Si of 0 to 5 ppm or less. The method of claim 13,
The copper-ceramic substrate (1), characterized in that the copper layers (3, 4) as a whole have a ratio of elements of As, Co, In, Mn, Pb and Si of at least 1.0 ppm and 20 ppm or less. The method according to any one of claims 4 to 14,
-A copper-ceramic substrate, characterized in that the copper layers (3, 4) have a ratio of B, Be, Cr, Fe, Mn, Ni, P, S elements of 0 to 10 ppm or less in each case (One). The method of claim 15,
The copper-ceramic substrate (1), characterized in that the copper layers (3, 4) have a ratio of B, Be, Cr, Fe, Mn, Ni, P, S elements of at least 1.0 ppm and 50 ppm or less as a whole. The method according to any one of claims 4 to 16,
-A copper-ceramic substrate (1), characterized in that the copper layer (3, 4) has a proportion of the elements mentioned in claims 7 to 16, not more than 50 ppm, including additional impurities.

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